The word "centralize" in the way you're using it is very misleading. Every piece of programming in existence uses some sort of language.

What you're really stating, I think, is that this is written in Javascript and you don't like Javascript. That's totally fine, and it's your prerogative. I'm sure that, like any other piece of programming, GitTorrent can be rewritten in other languages. If Javascript bothers you that much, then do this: rewrite it in Ruby if that's what you prefer.

But please stop attacking the claim that this is "decentralised github" by claiming that this "centralises" on Javascript. It doesn't "centralise" on any language. It's just a first implementation written in Javascript.